The invention relates to a method and a device for measuring the angle of inclination on laterally inclined bends.
In determining or assessing a driving situation within the scope of a vehicle dynamics stability controller, such as in ESP (Electronic Stability Program), errors arise in evaluating the vehicle state when traversing a laterally inclined bend which is distinguished by a side tilt with respect to the horizontal. One reason for this is the fact that parameters which characterize the respective vehicle state are additionally influenced by gravitation or centrifugal forces. A laterally inclined bend can be traversed in the extreme case without actuating the steering wheel. A vehicle dynamics stability controller perceives absence of the steering wheel displacement, but detects a rotation rate with reference to the Z-axis and a lateral acceleration with reference to the Y-axis. The result of this is that the vehicle dynamics stability controller is activated and initiates incorrect interventions in the vehicle dynamics. Instances of incorrect tripping of motor vehicle safety systems can also occur. For this reason, it is necessary in the extreme case, for example, for the ESP to be switched off by the driver when a laterally inclined bend is being traversed.
DE 43 25 413 C2 discloses a method for determining parameters which characterize the driving condition of a motor vehicle, such as rotation rate, lateral acceleration, steering angle, speed, acceleration, wheel speeds etc. The angle of inclination is required here as a state variable for exact calculation of the vehicle state.
However, it is disadvantageous in this case that no indication is given of how an angle of inclination is detected qualitatively or quantitatively.
Various methods are known for detecting the vehicle inclination and/or the roadway inclination with respect to the horizontal.
EP 0 769 701 A1 discloses a device for a vehicle which contains two acceleration sensors. These two acceleration sensors are arranged at a defined angle to the horizontal plane. Without vehicle inclination, the acceleration sensors indicate the same deviation from the vehicle lateral acceleration actually present. It is possible for the vehicle inclination, and from this the actual vehicle acceleration, to be calculated in accordance with the vehicle inclination by forming the difference and sum of the two sensor signals.
However, it is disadvantageous in this case that a plurality of acceleration sensors are required, and that these acceleration sensors serve only to detect a side tilt of the motor vehicle. This solution turns out to be very cost intensive. Again, it requires additional space. A further disadvantage consists in the two identical, but differently installed measuring systems do not reliably detect the correct angle of inclination of the roadway in every driving situation, and falsely indicate an angle of inclination in the case of swerving or roadway bumpiness.
Another method for determining the roadway inclination in the longitudinal direction is disclosed in DE 44 43 522 A1. Here, a freely rolling state, at least of one driven axle of the vehicle, is detected at least once. In this state, the wheels of the driven axles also roll without slipping. The differential speed of a non-driven axle is determined for the purpose of balancing the wheel speeds between the driven axles. The value of the braking ratio, that is to say the vehicle deceleration, is measured simultaneously. The values determined for the differential speed and the braking ratios are used to determine the value of an inclination constant. The roadway inclination can be determined with the aid of the inclination constant from the values determined for the differential speed and braking ratio.
It is disadvantageous in this case that only the inclination of the roadway in the longitudinal direction can be measured, and that a freely rolling state must be brought about for a measurement, in order to detect a roadway inclination at all.